The present invention relates to methods for determining the concentration of fluoride in gases. In an industrial setting, such gases result from electrolytic processes for production of aluminum by electrolysis of alumina in a molten cryolite bath.
Processes for measuring gaseous fluoride concentrations are known in the prior art. However, each of these prior art processes suffers from one or more serious disadvantages making it less than completely suitable for its intended purpose.
For example, one prior art process in commercial use prior to the present invention relied upon mixing a sample of fluoride-containing gas with water in a gas scrubber to form a fluoride-containing solution. A known concentration of bromide ion was then added to the solution, and the concentration of fluoride ion was measured in a potentiometric apparatus.
In this prior art process, error was introduced by evaporation of water in the scrubber. An attempt to compensate for this error resulted in the introduction of error caused by loss of mist from the scrubber. This prior art process was also sensitive to variations in the flow rate of water to the scrubber.
It is a principal objective of the invention to provide a method for determining fluoride concentration in a fluoride-containing gas, wherein the method eliminates errors caused by evaporation of water from the gas scrubber and of water supplied to the gas scrubber.
It is a related objective of the invention to provide a method for determining fluoride concentrations in a gas that avoids introduction of other errors.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification, taken in conjunction with the drawing.